Fabric Finishing Process and Treatment

After fabrics are dyed and/or printed in a process house, specific treatments can be given to impart and/or enhance fabric performance characteristics.

Knitting / Weaving

Bleaching

Dyeing / Printing

Fabric Treatments

Finished Fabric

Controlling Fabric Shrinkage

• Yarns are under constant tension during the weaving or knitting process. They will always try to shrink back to their natural state.

• Fabrics are therefore treated to minimize subsequent shrinkage. This is done by various processes such as cold and hot water immersion, steaming, mechanical compression by passing fabric through rollers, and – especially for wool - chemical and resin treatments.

• Sanforization is a process of treatment used mainly for woven cotton fabrics and also other textiles made from natural or chemical fibers. It is a method of shrinking and fixing the woven cloth in both length and width, which ensures the fabric will shrink no more than 5% after it is washed for the first time, as opposed to a potential 10% for un-sanforized fabrics. The machine used is called Zero-Zero pre-shrinking machine.

• For knitted fabric, a compacting machine – or compactor - is used. This accepts fabric in all knit structures in both open width & tubular forms. The machine controls shrinkage, sets the grain line, controls fabric gsm and gives the fabric a lofty hand-feel. The process is called compaction.

• Even after the fabrics are pre-shrunk using the above processes, they will still shrink further on laundering. This is called residual shrinkage. The industry commonly accepts a residual shrinkage of 3% X 3% for woven fabrics, and 5% X 5% for knit fabrics.

Mercerizing

• Used for cotton and linen, mercerizing causes the flat, twisted, ribbon-like fibers to swell into a cylindrical or oval shape and contract in length.

• The fiber becomes very lustrous (almost silk-like), its strength increases about 20%, and its dye pickup is greatly improved. At times a low concentration mercerizing is done solely for the improved dye pickup.

• The process consists of passing the fabric through a cold 15-20% solution of caustic soda (sodium hydroxide), then stretching it on a tenter frame, where hot water sprays remove the caustic.

• Both yarn and fabric can be mercerized. Cotton sewing threads are always mercerized for strength.

• Today chino pants are in demand – these are made from cotton twill that has been pre-shrunk and mercerized.

Nap Fabric

• Napping is a finishing process applied to one or both sides of a woven or knitted fabric, which raises the fiber ends to the surface of the fabric. The process is also called brushing.

• The fabric is passed under a roller which has fine steel or ceramic wires with small hooks at the end which pull up the fibers. All the raised fibers will lie in one direction. These raised fiber ends can then be clipped (sheared), flattened or left erect. A surface texture is created & the fabric becomes softer, dulls in color, and provides warmth by trapping air for insulation.

• A napped fabric will appear to be of different shades when viewed from different angles.

• It is very important to cut the garment panels with the naps going in one direction only. If a velvet gown is not cut with all the pattern pieces going in the same direction, the dress will look like it was made with two different colored fabrics.

• Napping will generally weaken the fabric. Napping can hide fabric and construction imperfections, and stains can be removed more readily from the surface. If a sueded (or peached) surface is required, fabrics are given a sanding by passing them through emery covered rollers.

How to Determine Direction of Nap?

To determine the direction of the nap, prior to layout and cutting, one should run the hand over the surface of the fabric parallel to the selvage. The fabric feels smooth when it is stroked with the nap and rough when stroked against the nap.

Pile Fabric

• Pile fabrics are woven (or knitted) with an extra set of yarns to produce a pile on one or both sides of the fabric, which creates their raised surface.

• Towels, carpets, rugs & velour, are made by interlacing a secondary yarn through the woven cloth, creating a pile.

• Pile fabrics are often loosely referred to as napped – but this is incorrect because they have not undergone a finishing process to make them true napped fabrics.

• Some pile fabrics may require a subsequent nap process like shearing (cutting) or brushing.

Shearing

• Is the removal of protruding ends of threads, knots, and hairs from the surface of a fabric, and making the length of the pile very even to improve the fabric’s visual appearance and hand-feel.

• Both woven and knitted fabrics can undergo shearing. The process is carried out on shearing machines.

Bio-polishing

Bio-polishing or enzyme washing removes the protruding fibers of a fabric through the action of an enzyme.

Calendaring

Calendaring makes one or both surfaces of the fabric smooth and shiny. The fabric is passed to through hot, fast-moving stainless steel cylinders that polish the surface and make the fabric smoother and more lustrous. Fabrics that go through the calendaring process feel thin, glossy and papery.

Crease-Resistfinish

Crease-Resist finish or "wash-and-wear" or "wrinkle-free" or “permanent press” finishes are achieved by the addition of a chemical resin finish.

FabricWicking

• Moisture-wicking fabric is used in workout clothing and sportswear because the material pulls moisture away from the skin. It is also used to make casual and business clothes for use in hot and humid conditions.

There are two major factors that make a wicking fabric work:

1. Capillary action

2. Water Repulsion.

• All wicking materials use capillary action to pull moisture away. Sweat dissipates throughout the material. Areas with a lot of moisture will 'bleed' the liquid to other less moist areas.

• To further aid the 'wicking' process, the fibers are coated with a water-repellent e.g. Gore-tex. The sweat tends to bead up to the fabric surface instead of being absorbed into the fibers.

SoilReleaseFinish

All fibers get soiled but most of them can be washed clean with detergents, soap & water which penetrates to the fiber. However, problems can arise with fabrics which are hydrophobic and oleophilic (oil attracting) – e.g. polyester.

Fluorocarbon and nanotechnology are the commonly used soil release finish in the textile industry. Read more.......

WaterproofFabrics

• They are resistant to wetting and penetration by water, either inherently or by processing. They are usually natural or synthetic fabrics that are laminated to or coated with a waterproofing material such as rubber, polyvinyl chloride(PVC), polyurethane (PU), silicone elastomer, and wax.

• Waterproof fabrics are breathable and they resist liquid water passing through but must allow water vapor to pass through it. They use for making rainwear and waterproof outdoor sports clothing.

• Taslan is a lightweight, durable and water repellent nylon fabric with a slightly shiny surface.

Anti-pillingfinish

• Anti-pilling finish alleviates pilling, which is the formation of unsightly balls of fiber forming on the surface of spun-yarn fabrics, especially when they contain synthetics.

• Synthetic fibers are more readily brought to the surface of a fabric due to their smooth surface and circular cross-section, and due to their higher tensile strength and abrasion resistance. The anti-pilling fabric finish greatly reduces this problem.

Anti-staticfinish

• Anti-static finish prevents dust from clinging to the fabric, and this also gives a good soil release action.

• The US company NANOTEX has developed nano-technology for 5 key textile technology segments:

1. Stain repellence & stain resistance

2. Moisture management

3. odour control

4. Static elimination

5. Wrinkle-free

Anti-bacterial finish

• Clothing and textile materials are carriers of micro-organisms such as pathogenic bacteria, odour generating bacteria and mould fungi, and also a media for the growth of these microorganisms.

• Antibacterial fabric resists colonization by bacteria and reduces the risk of spreading infection and developing unpleasant odours. It can be used in health-care settings to protect patients and is also used in products like sports clothing and bedding which are prone to contact with sweat.

• Nanoparticles, particularly silver, are used in some antibacterial fabrics. These can confer long-lasting protection against unwanted organisms. Upgrade®-silver finish is an antibacterial finishing technology using active silver ions. The finish is long lasting and washes resistant.

UV-protection

• Ultra Violet radiation can lead to acute and chronic reactions and damage, such as skin aging, sunburn & permanent skin damage.

• Coating the surface of textiles and clothing with nano-particles gives UV blocking properties. Zinc oxide {ZnO} nano-particles embedded in polymer matrices like soluble starch can be used and is more stable compared to organic UV blocking agents.

• Use of a mixture of titanium dioxide and zinc oxide in a 67:33 proportion during fabric processing is capable of giving a UPF > 50.

• AATCC 183 method defines the UPF (ultraviolet protection factor) rating for a fabric as the ratio of UV measured without the protection of the fabric compared to the UV with the protection of the fabric.

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